1. Field of the Invention
The present invention relates to a polyether ester elastomer. More particularly, the present invention is concerned with a polyether ester elastomer comprising a copolymer of (A) at least one aromatic dicarboxylic acid or an ester-forming derivative thereof, (B) at least one diol selected from the group consisting of an aliphatic diol and an alicyclic diol, each having 2 to 10 carbon atoms, and (C) a polyoxytetramethylene glycol (PTMG) having a specific number average molecular weight, a specific molecular weight distribution, a specific content of high molecular weight PTMG molecules, and a specific heteropolyacid content, wherein the polyether ester elastomer contains PTMG units in an amount of from 10 to 90% by weight, based on the weight of the polyether ester elastomer. The polyether ester elastomer of the present invention contains a soft segment composed of a specific PTMG having not only a high heat resistance, but also a low viscosity. By virtue of the presence of such a soft segment, the polyether ester elastomer of the present invention not only is improved with respect to the properties essentially required for an elastomer, such as low-temperature characteristics, flexure resistance, abrasive resistance and elastic recovery, but also has other excellent properties, such as high mechanical strength and elongation, small permanent compression set, high softening temperature, excellent mold release characteristics exhibited during injection molding thereof, and no tack on the surface of the ultimate shaped articles, which have not been conventionally achieved in the art.
2. Prior Art
A thermoplastic polyether ester elastomer is a polyether ester block copolymer comprised mainly of polybutylene terephthalate (which forms a hard segment) and polyoxytetramethylene glycol (which forms a soft segment), and exhibits rubber-like elasticity and weatherabiltiy. The fields in which the thermoplastic polyether ester elastomer is used have been increasing, and the thermoplastic polyether ester elastomer is now used in various fields, such as the fields related to electric and electronic parts, automobile parts, fibers and films.
At present, polyoxytetramethylene glycol (PTMG) is widely used for forming a soft segment of a polyether ester elastomer. However, depending on the molecular weight and molecular weight distribution of the PTMG employed, the final polyether ester elastomer may have the following problem. Due to the linear structure possessed by the PTMG, the PTMG contained in the polyether ester elastomer may sometimes be crystallized at low temperatures and, thus, the properties (such as characteristics at low temperatures and elastic recovery) of the polyether ester elastomer become unsatisfactory depending on the conditions under which the polyether ester elastomer is used. In order to solve this problem, attempts have been made to produce a raw material PTMG having a narrower molecular weight distribution (Mw/Mn) and a relatively low number average molecular weight (Mn) (see Unexamined Japanese Patent Application Laid-Open Specification Nos. 54-158497 and 60-55027).
As a conventional technique for obtaining a PTMG, a method disclosed in Unexamined Japanese Patent Application Laid-Open Specification No. 59-215320 (corresponding to U.S. Pat. No. 4,568,775) is known. Further, Unexamined Japanese Patent Application Laid-Open Specification No. 61-123626 (corresponding to U.S. Pat. No. 4,658,065) and Unexamined Japanese Patent Application Laid-Open Specification No. 59-221326 (corresponding to U.S. Pat. No. 4,568,775) have a description concerning the molecular weight distributions of the produced PTMG""s. With respect to the techniques for removing the oligomers contained in a PTMG, Unexamined Japanese Patent Application Laid-Open Specification No. 61-123629 (corresponding to U.S. Pat. No. 4,677,231) discloses a method in which a thin film evaporator is used, and Unexamined Japanese Patent Application Laid-Open Specification No. 60-108424 discloses a method in which oligomers are separated from the PTMG by using water and an alcoholic solvent. In addition, with respect to the techniques for adjusting the content of a polymerization catalyst remaining in a PTMG, Unexamined Japanese Patent Application Laid-Open Specification Nos. 61-118420 and 61-115934 (both corresponding to U.S. Pat. No. 4,677,231) disclose a method in which a hydrocarbon or a halogenated hydrocarbon as an organic solvent is added to a PTMG to thereby separate the residual catalyst therefrom; and Unexamined Japanese Patent Application Laid-Open Specification No. 61-123629 (corresponding to U.S. Pat. No. 4,677,231) discloses a method in which an adsorbent is used to remove the catalyst.
The characteristics (such as molecular weight, molecular weight distribution, oligomer content and residual catalyst content) of the PTMG used as a raw material for a polyether ester elastomer are important factors which affect the quality of the final polyether ester elastomer. However, heretofore, no details are known in the art about how the characteristics of the PTMG influence the properties of the final polyether ester elastomer. In addition, no polyether ester elastomer are known, which have been adjusted, by strictly controlling the characteristics of the raw material PTMG, so as to have a good balance of various excellent properties.
Nowadays, the polyether ester elastomer is an important material which is used in a wide variety of fields, and the application field thereof is expected to become more extensive. Accordingly, there has always been a demand for improvement in the quality of the polyether ester elastomer. Further, improvements in different properties of the polyether ester elastomer are, respectively, desired in different application fields.
In this situation, the present inventors have made extensive and intensive studies with a view toward developing a novel polyether ester elastomer which has not only an improved rubber-like elasticity, but also a good balance of various excellent properties. As a result, it has unexpectedly been found that, when a polyether ester elastomer is produced by using a PTMG which has a specific molecular weight, a specific molecular weight distribution, a specific content of high molecular weight PTMG molecules and a specific heteropolyacid content, and which has not only high heat resistance, but also low viscosity, the produced polyether ester elastomer not only is improved with respect to the properties essentially required for an elastomer, such as characteristics at low temperatures, flexure resistance, abrasive resistance and elastic recovery, but also has other excellent properties, such as high mechanical strength and elongation, small permanent compression set, high softening temperature, excellent mold release characteristics exhibited during injection molding thereof, and no tack on the surface of the ultimate molded articles. Such properties have not been achieved in the art. The present invention has been completed, based on this novel finding.
Accordingly, it is an object of the present invention to provide a polyether ester elastomer which has a good balance of various excellent properties.
The foregoing and other objects, features and advantages of the present invention will be apparent to those skilled in the art from the following detailed description and appended claims taken in connection with the accompanying drawings.